There are many applications in which it is necessary or desirable to join a movable structure to a fixed structure to provide access to the movable structure while allowing movement of the movable structure relative to the fixed structure. For example, it is often necessary to provide access between a ship and a pier or an aircraft and an airport terminal. This is particularly a problem for motion-bases that typically include a "base" or platform that can provide for six degrees of freedom of motion including roll, pitch, yaw, vertical, lateral and longitudinal motion. Motion-bases are widely used in devices such as vehicle simulators, amusement rides and interactive theaters which move in synchronization with images projected on a screen to create the illusion of riding in a particular vehicle.
It will be readily appreciated that the complex movement of the motion-base makes it impossible to use rigid bridges having fixed dimensions and orientation to join it to a fixed structure. Moreover, a bridge or gangway that is not anchored at one end but in sliding engagement with the motion-base or the fixed structure, such as a brow joining a ship to a pier, is also generally not satisfactory because it cannot allow for simultaneous rotation about or movement along multiple axes. For example, while a ship's brow is frequently made to allow for some lateral motion away from and toward the pier, and may even be hinged to allow for moderate rolling motion, it would not allow for a pitching motion that would cause opposite sides of the brow to lift alternately. Thus, prior art solutions for providing ingress and egress to a motion-base while allowing it to move relative to a fixed structure have focused on movable ramps or platforms moved into position after the movement has been stopped to allow access to and from the motion-base.
One proposed solution, shown in FIGS. 1 and 2, utilizes five parallel planks 20 extending from the fixed structure 25 to the motion-base 30 to form a gangway 35. The planks 20 are joined to one another by an tongue-and-groove arrangement 40 that allows adjoining planks to be moved in opposite directions as indicated by arrows 45. Each plank 20 is coupled to either the fixed structure 25 or the motion-base 30 in such a manner that no two adjoining planks are both connected to the same structure. The planks 20 are rigidly connected to the fixed structure 25 through a first bar 50, and are connected to the motion-base 30 through a second bar 55 and a pivot 60. While an improvement over ramps which are manually moved into position this design is not completely satisfactory.
A problem with this approach is it severely limits the freedom of movement of the motion-base 30. In particular, the rigid attachment to the fixed structure 25 prevents the gangway from allowing longitudinal movement of the motion-base in a direction perpendicular to the gangway 35. For the same reason, the gangway 35 does not allow a yawing motion or a purely vertical movement of the motion base 30. This design might allow a limited rolling motion of the motion base 30, provided the roll axis coincides with the axis of the pivot. In fact, the only movement of the motion base 30 that the gangway clearly would allow is a lateral movement towards or away from the fixed structure 25. A further problem with the gangway shown in FIG. 1 and FIG. 2, is the difficulty and expense of forming the tongue and groove arrangement 40. Moreover, this design allows dirt or other foreign objects to fall into the tongue and groove arrangement 40, which can cause the planks 20 to bind and rendering the gangway 35 inoperable.
Another prior art solution, as disclosed in U.S. Pat. No. 5,277,662, to Fox et al., hereby incorporated by reference, use movable platforms pivoted into position to load and unload passengers from a motion-base, here an amusement park ride, and folded away from the motion-base while it is in operation. Although this approach avoids many problems of rigid bridges and sliding gangways, it leads to several additional problems, and therefore is also not completely satisfactory.
One problem with this approach is the added cost and complexity of a controller required to return the motion-base to a precise position relative to the fixed structure. The controller is also needed to synchronize the movement of the platform to that of the motion-base so that the platform is moved into position as soon as the motion-base stops. In addition to the cost, the controller also adds to the maintenance requirements and the potential for malfunctions. Moreover, for many applications, such as an amusement ride, the time delay occasioned by extending or folding away the platform before and after operation of the motion-base is very undesirable.
Another, more serious problem with all such solutions is that the passengers are effectively trapped on the motion-base for the duration of the ride. While many passengers would probably be unaware of this, or at most would be only slightly inconvenienced, in case of fire or a medical emergency the situation could be life-threatening. Moreover, if, as in the reference cited above, the platform is automatically or electronically controlled the problem is exacerbated during a power failure.
Yet another problem with the above approach, is the potential for injury by the movable platform. If the platforms do not couple with the fixed structure or the motion-base closely enough, a passenger can fall through or have a limb or clothing become trapped in the resulting gap.
Accordingly, there is a need for an apparatus and method for joining a movable structure to a fixed structure to provide access to the movable structure while allowing movement of the movable structure relative to the fixed structure. The present invention provides a solution to these and other problems, and offers other advantages over the prior art.